1. Field of the Invention
This invention relates to a glass antenna for a motor vehicle, more particularly, to a glass window antenna which applies reception power to a receiver in a diversity reception system.
2. Description of the Prior Art
Reception condition varies in accordance with movement of reception point when an FM or TV broadcast wave is received by a traveling motor vehicle. A space diversity reception system using a plurality of antenna elements is employed to prevent quality of radio voice or TV picture from being degraded due to the variation of reception field. It is known to constitute these antenna elements for diversity reception with glass window antennas formed of conductors printed on a window glass of the motor vehicle (refer to, for example, Japanese patent application laid-open No. 203702/1986).
The glass window antenna is usually arranged on a rear glass window due to convenience to keep field of view of front windshield as well as problem of wiring between the antenna and a receiver
A space to arrange the antenna conductor is however limited to upper or lower blank portion outside the middle area where defogging heater wires are attached with printing. Many antenna conductors can not be provided on a glass window having small blank areas. Especially, a small-sized automobile has an upright rear window with less blank area to arrange necessary antenna conductors thereon. Moreover, when many antenna conductors are arranged in the blank portion, they must have simple configuration with few constitutional elements. It restricts tuning factors of reception directivity and bandwidth.
Accordingly, it is an object of this invention to arrange antenna conductors having high efficiency for diversity reception on a limited area of glass window.
It is another object of this invention to provide arrangements of antenna conductors which can be incorporated with a space and frequency diversity reception system.
A window glass antenna for a motor vehicle according to this invention comprises a group of heater wires provided in a defogging area on the inside surface of a laminated window glass consisting of an inner glass and an outer glass; a first antenna conductor arranged out of said defogging area on the inside surface of the inner glass; a second antenna conductor inserted into an intermediate layer of the laminated glass and extending to cross the heater wires; and a coupling member to couple said first and second antenna conductors for constituting a single synthesized antenna; the first antenna conductor being assigned to a lower reception band and said second antenna conductor being assigned to an upper reception band.
The first antenna conductor shows sufficient gain with relatively simple conductor pattern since it is limited to reception of lower reception band, though conductors are hard to be patterned into a complex form for tuning on a narrow blank area. The second antenna conductor is insulated from hearer wires through a glass so that conductor can be a vertical element crossing the heater wires. A vertical element amounted on a motor vehicle can be easily tuned in higher frequency band.
The synthesized antenna consisting of the first and second antenna conductors coupled with each other has good reception characteristics over a wide frequency range. An antenna system which effectively uses a narrow space on the window glass is obtained.
The above, and other, objects, features and advantages of the present invention, will become readily apparent from the following detailed description thereof which is to be read in connection with the accompanying drawings.